How long as he been at 1u? I'm taking it that this was a recent increase, so I would go ahead and give him the 1u if you are going to be around to monitor him this evening. Since he is still above 200 he has a bit of wiggle room to drop down. However, if you need to be gone tonight and aren't comfortable with giving that full 1u you can shoot the .5u and get back on track tomorrow with the 1u. He will probably be higher tomorrow if you go with the .5u but I would rather see him higher tonight if you are going to be away than going to low without you there to keep an eye on him.
Lantus does like a consistant dose whenever possible but it also has to be balanced with not killing the bean from worry.
Mel, Maxwell, Musette & The Fur Gang