Slightly laggy from what I have read, but thats because most have a FMIC. You will need at a minimum a Downpipe, up pipe, injectors, fuel pump, bigger intercooler and a tune. There are some other things that can be added also, but thats the minumum.
defiantly stick to the TD05 housing for the EJ205. The TD05-20G is pretty big, I wouldn't bother with it if you're going to run pump gas, particularly 91 or 92. An 18G will have less lag and you're not going to top out either anyway.
well from the past week of having my car back on a FP Green which is the larger TD06 housing I'm happy to report that the lag is no where near as bad as expected...I'm seeing 20psi by 4200 RPM...my advice to you if you do go with a larger turbo on a 2.0 make sure you P&P the exhaust manifold like no tomorrow!