If you can, get a +11 (or +11.5) .....it'd help to know if he's still rising at AMPS time
If he bounces (like over 300) you can give one more dose at 3U (it's called "shooting through the bounce) to give him a little more support to get back down, but if he's less, I'd take the deduction to 2.75
It also makes a difference if you're going to be home and able to test
In the future, if you get a test you're not sure about, stall...don't feed, and post for help. Lantus works best when it's given at lower numbers (Once you have the data to know it's safe) so you gradually shoot lower and lower Pre-shot numbers.