An update to this.

Since it looks like I'll be redoing my timing anyways, I'm going to pull the head.

Something that I've been thinking of and has been mentioned by a few others during discussion as well is the possibility that I'm pushing exhaust into the coolant under boost, which would explain why the car stays at temp idefinitely while idling but heats up *instantly* after even a bit of boost (especially a pull). I've also been seeing coolant dripping out the overflow hose lately, which also lends credence to that idea.

To clarify: When I say 'instantly' I mean the coolant temps are at ~180, if that, ambient temps are < 6C, and after ONE pull to mid 4th the coolant temps are mid-high 220's.

Although the engine had a new OEM head gasket when I bought it (or so I was told), I have no idea if copper spray was used or not or if the surfaces were properly prepped. This will be a pain in the ass but peace of mind is priceless. Nothing else left that anyone has mentioned or can think of that would cause my issues.

I'll have to pick up some copper spray and some ARP lube, and possibly a new headgasket pending inspection.