Best used road bike to buy with view to upgrade

I have been looking at getting a new road bike but looking at other options too. With that in mind what bike would others recommend to buy in good working condition second hand, which would have a good frame, prefer steel or alloy, which I good upgrade groupset to 105, new wheels, tyres as and when i could afford to upgrade.
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2. The best material. 531 or the equivalent and up.
3. A bargain.
4. A paint job you like.
Something that meets all of the above.
I am not sure. You have no chance.
Well if i was buying new I would be willing to spend up to £800, for a used bike with a view to upgrade from around £250 to £400 otherwise I might as well buy new.
Decided on a new bike in the end yesterdday, Tredz was having a mayday sale and I got 15% discount off a new Giant Contend SL 2, not quite Ultegra but Tiagra.