Hello again Ron,
Regarding your lens, I've checked the 'net on these and these lenses seems quite cheap. The Pentax at Â£50 is a good price. I've no doubt the Tamron is OK and if you're not going to use it often then fair enough. I have an old Tamron 70-200 Adaptall 2. I've used this with Pentax, Nikon and Minolta mounts with nice results. I would say the Pentax glass is superior, especially as Hoya now own Pentax. My zoom nearest to this is the Sigma DL Macro Super. Stick to Pentax.