If memory serves, this BNR 68HTA uses a 7.5 cm compressor. I picked this up when they were first released. The 7 cm compressor seems to correlate to higher peak torque than those with 7.5 and 8 cm compressors. My peak torque is a very respectable 368 ft/lbs. The HTA68 can flow alot of air under higher boost pressures.
With E85, mine peaks at 23.5 psi and tapers to around 20 psi at redline. Because of that, a TMIC with improved flow can help optimize performance more than you might see with lower boost targets. But that doesn't mean that you wouldn't see a notable gain running 93 octane and lower boost targets.
When I was running a Perrin TMIC at Stage 2 with a Protune on 91 octane, it was around 20 whp more than comparable cars on the same dyno on the same day using the same tuner. Torco race gas tunes using the factory TMIC were about the same as what I was getting with the Perrin on 91.
So, the moral of the story is pretty simple. An intercooler with better flow is very likely to provide you with a respectable bump in performance. They are not just window dressing. Are they worth the investment? Some would say yes and others would tell you to invest in headers, alcohol injection or any other number of things.
I would expect the GS TMIC to be an improvement over the Perrin design but for me, it is as much about quality as it is output. I literally hate taking the Perrin off with putting it back on being even worse. If it is better for maintenance, I'm all too happy to give them my money. If it opens up other turbo options and it provides better performance, that is all gravy to me.