Bit of advice if it's a not a daily just a fun car 400 bhp will be fine reliable and you can use all of that power....

No point in having 600+bhp if your not going to use it!!!
There are plenty of Willy (small) wavers in the cosworth scene who's cars will never see a strip or track or get used in anger Or a top speed attempt.

470 bhp can be had with limited engine mods and a modern turbo ecu etc.

Remember it's old tech and there are more modern capable cars out their for Less cash.

Your choice.