I have
2 x 6000 GTE C
8 x 10000 GTE C
4 x 10000 XTE A
New ranges in the more affordable ranges:
ST - 2 Bearings and spool oscillation is geared so one turn up on turn down. Single ABS spool, R480
DL - is the deluxe version of the Geared ST and has an alu and an ABS Spool R600
XT - few more bearings in it with 2 x Alu Spools, also geared and the spool has the aero lip that draws air in under the line lifting it off the below layers to cast better. R950
XTRA, is the replacement of the XTEA and is the Super Baitrunner. It's oscillation is one turn up and 2 turns down making for aero line lay which prevents line hooking onto itself it then also has the areo lip spool to add to casting proficiency, Plenty bearings 6 or 7. R1450
6000 and 8000 body size is the same only spool capacity differs and the spools are inter-changable
10000 can be used with 6000, 8000 and 10000 spool. 10000 spool can be used as a mini big pit as it holds 600m+ of 30lbs and 750m 20lbs braid
(10000 spool can't be used on the 6000/8000)
The XTRA is an upgrade on the XTEA which had a few problems in terms of parts that were just glued on and often the worm gear alignment was not right and line would taper on the spool. If you put the 2 alongside one another it merely looks like a colour variation.
Price variation is just as a result of the difference in number of bearings, spool types, spare spool types (etc) and gearing systems etc.
I personally fish my 10000 on 8', 10', 13', 15' rods as it has the highest retrieval rate and one body accepts all spools, on the 8' I use the 6000 spools of my GTE's to slow retrieve down a bit.