is bad to run plugs that might be too cold?

This weekend I bought some Autolite 103's and I plan to run a 100 shot and eventually a 150 shot this summer...are they too cold ? and will they affect my NA perfomance or mpg alot??
I might just get the 104's also and swap them for the 103's when I increase the shot to 150.
or can I just stay with the 103's?
what do you think?

Thanks!

actually the 103 is colder then the 104. but you wll be ok either way. with tr6's i noticed no loss in mpg,and n/a et didnt suffer at all.

sounds good! Thanks alot!

For a 100-150 (relatively small shot), you should only need to go one step colder. NGK TR6's are the way to go. If you go too cold, it will take the plug longer to reach self cleaning temp and could they could start to fould with a lot of short trips. ive never had any problems though. and be careful with the gap. the stock gap is at .065 on mine, and i went with a .36 gap for a 125 shot. watch the tioming too...

I ran my best NA time so far on Autolite 103's. So I'd say the 103's are fine. :)