TD05 18G slightly smaller,
anything bigger than that in Trust is going to be in a high mount application.
TD06-25G / T67 would be similar, T67 8cm is hella responsive on an RB25 (Trust make these for SR20), but you will be going external gate and high mount.
T517 single on RB25 is not going to cut the cheese im afraid.
Becides the T25 flange, its going to run out of puff too quickly if you want to compare it to a GT-RS.
a 10cm T517 might get you there, but again different flange
If high mount is not a problem, perhaps look up the scale into the TD range from Trust.
If you want to keep it low mount, theres GT-RS or perhaps do some dealings and see if you can get a larger rear housing for TD05-18G? (not sure if this is a possible option)
There is also the TD06Sh 20G with 14cm internal gate (something I've never seen from trust) Their largest internally gated turbo.