I have too much time on my hands so I thought I'd put this info together to compare some of the differences between the Fantom G and Fantom X. Info listed first is Fantom G and the info after is comparing to Fantom X.
Fantom-G: Workstation Keyboard
Reaching New Levels of Power and Luxury
Relative Comparison between the new Fantom G and the older Fantom X series: (Note! There may be a
few discrepancies because of Roland's lack of specificities regarding the Fantom X specs on their web site). Also there may be a few errors on my part because of my lack of experience regarding some of the Fantom X features and how they work.
Specs
Keyboard and Sound Generator Section Keyboard
88 keys, PHA II, Ivory feel, with velocity and channel aftertouch --- >> New keybed on 88 key version.
76/61 keys, velocity and channel aftertouch --- >> Same as Fantom X with same keybed??
Mamimum Polyphony
128 voices, shared with the sampling section --- >> More parts on Fantom G; over 3 times the amount when including ARX and Audio Tracks.
Wave Memory
256MB (16-bit linear equivalent) --- >> Double of the Fantom X
BUT a fully loaded Fantom X has almost 1 gig of wave memory with SRX expansion etc.
Waveforms
2,153 --- >> 673 more Waveforms than the Fantom X
Preset Memory
Patches 1,500 + 256 (GM2) --- >> 348 more Patches than the Fantom X
Rhythm Sets 64 + 9 (GM2)
Live Sets 512
Studio Sets 128
User Memory per one project
Patches 512 --- >> Double the User Memory Patches over the Fantom X
Rhythm Sets 64
Live Sets 512
Studio Sets 128
Effects
Patch Multi-Effects (PFX) 16 systems, 76 types
Multi-Effects (MFX) 2 systems, 78 types ---- >> Why is Roland so skimpy on their Fantom X specs??

They do not list..
Reverb 1 system, 10 types
Input Effects 1 system, 6 types
Mastering Effects 1 system, 3-band compressor
Data Format
16-bit linear, .WAV or .AIFF ---- >> ?? (When you consider that the Fantom X can
utilize up to 16 Phrase Tracks and each Phrase Track can have up to 16 MIDI tracks 'per' Phrase Track -
which equals 256 MIDI tracks total: So twice as many as the Fantom G)??
Audio track: max. 24 ---- >> (24 more than the Fantom X).

Tempo track: 1
Beat track: 1
Resolution
480 TPQN ---- >> (approx. 600,000 more notes than the Fantom X).
Song Length
9,998 measures ---- >> No sliders on the Fantom X.
Assignable Switch x 2 ---- (No assignable switches on the Fantom X??)
D Beam Controller ---- >> No D Beam on Fantom X.
Connectors Headphones Jack
Stereo 1/4 inch phone type
A (MIX) Output Jacks (L/MONO, R)
1/4 inch TRS phone type
B Output Jacks (L, R)
1/4 inch phone type
Input Jacks (L/MONO/MIC, R)
1/4 inch phone type
Mic./Guitar Input Jacks
1/4 inch phone type / XLR type (Phantom power)(Hi-Z) ---- >> No Mic. input or Phantom power on Fantom X.
Pedal Jacks
Hold Pedal Jack (Half Pedal recognition)
Control Pedal Jack (assignable) x 2 --- >> (1 more Pedal Jack than the Fantom X).
MIDI Connectors
IN, OUT, THRU ---- >> (USB 1.1 on Fantom X whereas Fantom G has USB 2.0 and can transfer Audio via USB Flash drive (not included

USB Mouse Connector --- >> No USB Mouse Connector on Fantom X.
Digital Audio Interface
COAXIAL INPUT / OUTPUT ---- >> Half of Fantom X's 256 Sets.
RPS Sets 32 ---- >> 32 (Groups) on Fantom X as well??
Rhythm Pattern Sets 32 --- >> Read above line..

Chord Memory 128 --- >> (Twice the Chord Memory of the Fantom X).
Chord Memory Sets 128 --- >> Exponential increase over the Fantom X.
Display
Graphic Type, 8.5", Wide VGA (800 x 480 dots), backlit LCD (Color) --- >> Much larger Display than the Fantom X.
Pads
16 pads, Velocity and Polyphonic Aftertouch sensitive --- >> No ARX expansion on Fantom X; but Fantom X has "4" SRX slots.
Expansion for sampling memory
DIMM: 1 slot, supports PC133, CL=2/3, 3.3 V, 128MB, 256MB, 512MB --- >> No USB Flash drive capability on Fantom X; but Fantom X can use a PC card
which (supports SmartMedia and CompactFlash).
Power Supply
AC 117 V, AC 230 V, AC 240 V (50/60Hz), AC 220 V (60Hz) --- >> (Fantom X does NOT support AC 220 V (60Hz); at least it's not listed on Roland Fantom X spec sheet if it does.)
Power Consumption
30 W --- >> Uses 13 "more" Watts than the Fantom X making it close to double the amount.
Accessories Owner's Manual, CD-ROM (Editor, USB MIDI driver), Power Cord
Options Expansion Board: ARX Series, Keyboard Stand: KS-V7 (Fantom-G7/-G6), KS-18Z
(Fantom-G8/-G7/-G6), KS-G8 (Fantom-G8), Pedal Switch: DP series,
Foot Switch: BOSS FS-5U, Expression Pedal: EV-5, USB Flash Memory: M-UF1G, M-UF128, Microphone:
DR series, Headphones: RH-series
Size and Weight Width
1,396 mm
55 inches
Depth
502 mm
19-13/16 inches
Height
183 mm
7-1/4 inches
Weight
32.0 kg
70 lbs. 9 oz. ---- >> 5 1/2 lbs. more than the Fantom X8.
Fantom G 76 key
Weight
36 lbs. 7 oz. ---- >>> 4 lbs. 7 oz. more than the Fantom X7.
Fantom G 61 key
Weight
32 lbs. ---- >>> 4 lbs. 7 oz. more than the Fantom X6.
*The specifications are subject to change without notice.