Like SageRatS, I had the same question.

What it boiled down to decision wise, cost was the same, I was only going to bench rest with the gun and Heavier is more stable even if I might be able to tell, and it does not hurt and may help (hot day and a lot of shooting though not likely in my locale)

So I went with the Bull, no regrets.

I have put the 308 Savage Varmint on my play gun and shooting side by side I am not seeing a heat build up difference though again temps here are significantly lower than many places and have not done so on what would be a hot day for us (70 deg)

I can say while the Bull take longer to heat up, it also takes longer to cool down.

The Varmint is in between, heats up quicker but also cools down quicker. Heat up means fairly warm, not hot so far.

Both shoot the same cold as warmer.