I wouldn't bother with a Shimano reel less than 3000 size. Body sizes are often (not always) the same through the ranges, the difference being in spool and rotor sizes. A wider diameter spool has a couple of advantages. One has been hinted at by Mark B, wider diameter giving bigger coils of line which helps when using any kind of line with "memory". Tight little curls are not a good thing.
The second advantage is that the wider spool brings the lip of the spool closer to your finger for casting and finger control when trotting.
Another point to consider is that Shimano match reels in 3000/4000 sizes often have shallow "match" spools which actually have less capacity than the 1000/2000/2500 size reels. Look out for the "S" suffix in the model number.
An example from the current catalogue is the Super GT RC
It's available in four sizes, 1500, 2500, 3000 and 4000.
The codes are SUP1500GTRC, SUP2500GTRC, SUP3000SGTRC and SUP4000GTRC.
The 3000 size has that "S" suffix indicating a shallow spool. the respective line capacities are 4lb/140m, 6lb/200m, 6lb/180m and 6lb/240m.