If speed isn't an issue, should I just stay with my std 250 on an FX21?
your the only one that can answer that.
as far as "other" benefits. more available power from an ecu flash means
1) quicker hole shots, reducing fuel consumption
2) quicker and more power at mid range means a tad higher speed at that mid range
3) of course top end is there when or if you want it.