Hi Nick,

I picked up a plain Takumar 135mm F2.5 recently (not realising it wasn't an SMC Super Takumar) and haven't heard any good things about it since (soft etc.)

Correct 100% on that one I am afraid. It is not considered as good as the other Takumars but remember for portaits this may be nice (soft). I am currently trying to sell mine as well!

Alternatively I have a cheap Series 1 F3.5 Vivitar 70-210 zoom arriving soon,

I have not used the Series 1 Vivitar 70-210 but have owened / used a Vivitar Series 1 35 to something. That was certainly a nice zoom for its day. IIRC the Vivitar Series 1 zooms were highly regarded here in the UK. But they were heavy and bulky. Give the 70-210 a try, I am sure you will be impressed.