Er, - I don't think a T25 Stage 1 needs an intercooler upgrade. I've got a stage 1 and it's fine with the standard intercooler. On the small turbo stage 1 is only an extra 40 bhp. GGR do a 300 brake conversion but even that retains the standard cooler, and by then you've maxed out the turbo MAF and injectors...

If you do fit one you may almost end up increasing the lag slightly because they'd be more air in the intercooler to compress.