Further development with my Wolfdale issue ... I've gotten 2 more r2.0 boards in the meantime.
One is r2.04, and the other is newer version of r2.03 (judging by the BIOS version it came with).
2.04 came with P4 641 and blown polymer cap just above the socket. I got cap replaced with the one with higher values (680uF -> 1000uF), put in E5800 ... and if fires up every time with no problems. Ran 3h of P95 for stability testing. No issues other than slightly off temp readings. So, Wolfdale problem solved finally 😀.
Still left to try newer 2.03.

Regarding 1066 FSB chips, I actually have good experience with that. Ran C2D Extreme x6800 with no issues. Yes, board "overclocks" itself, but it's also running memory with divider on that FSB ...177/355MHz , so you should not expect any issues with 400MHz sticks.
Tested with KHX CL2 400MHz sticks (Infineon BE-5). But most of 400Mhz sticks should do 355Mhz CL 2.5 with no problem.

EDIT: Just tested new r2.03 board, Wolfdale works.
To sum it up:
- r2.03 - BIOS P2.20 -11B - does not work
- r2.03 - BIOS P2.20-13A - works, but wonky
- r2.03 - BIOS P2.70-9A - works
- r2.04 - BIOS P2.90-9A - works

All boards were tested with P3.30 BIOS. Above noted BIOSes are the ones boards came with when new (sticker on a BIOS chip).
It seems support is better with newer 2.0x boards.