How much yeast?

[Whrrr]

I'm going to try Mr Wheeler's recipe for Sarah Hughes Mild. I'll be doing the extract version. The plan is to use Windsor yeast. The yeast packet says use for up to 23l but I'm going to do the 25l quantity. Bearing this in mind, together with the fairly high OG (1058 I think), should I use more than one packet of yeast? A whole second packet or maybe just half of it?

What can happen if you use too much yeast?

Thanks,
Mark

[Whrrr]

I've just found Mr Malty's yeast pitching calculator and it suggests 1.3 packets, so 1 and a half it is.

Should anyone else need it:

http://www.mrmalty.com/calc/calc.html