My DSLAM's a Huawei and my PCP's the newest style (if anyone could tell me what make these are that'd be interesting ;)). But I know G.INP is enabled as I've a HG612 on a Huawei modem, but I'm convinced there's some sort of problem between the cab and our house, as 600m isn't that far really, even when you take into account the VDSL drop off.
I just wish we had our own JDSU type device to find out this sort of thing!