Just about any accelerator card from 030/40MHz up will make your basic A1200 look ponderously slow.
If you have the funds and can find one, maybe you'd be better off betting a Blizzard 040, or even a BlizzardPPC..
OTOH, if youre not interested in PPC, you could try to get an 060. I read somewhere hereabouts that a supplier was selling the chips 'cheap' and you could (maybe still can) get the Blizzard 060 cards with a 060 socket.
I had an apollo 1240 some time ago and it was a troublesome beast. Having said that, it was an early revision...