I go with 800 ton Grav survey boats. Effectiveness of a survey ship is a balance of its speed, endurance and the cost of the payload. Since the cost of the survey sensor is fixed, the rest of the boat isn't going to add that much to the cost of the ship until you have much better engine tech.
If I am feeling extravagant, I push the size up a little bit, and give them a 1 HS sensor system. I have a survey support carrier, not to transport them long distance, but to repair anything out in the field, and to house the scouts and jump point probe pinnaces. I also drop monitor satellites on both sides of all jump points. Not really great sensors, just enough to detect anything close enough to transit. Most of the warning is from the enemy blowing them up.
Part of efficiency in survey operations is that if a system doesn't need to go all over the system, it shouldn't. So the jump tender should always be a commercial ship that helps the survey fleet transit. It doesn't even need to stick around at the entrance, although you could have an RP that it doesn't leave while there are ships in the system.
I am a big believer that solo survey ships are a horrible idea. You always wants something else in the system out of range of the enemy who can report the destruction of your survey ship, because that is information that you HAVE to know as fast as possible.
And a survey fleet simply has no chance of fighting off anything except an enemy scout. In the event of combat, any military systems should be aimed at simply getting more detailed information about the enemy capacity.
That can include recon missiles. Missiles with no warhead, that don't travel very fast, but have a very long range. They won't have a targeting system that can hit an enemy, but can go to a waypoint on the enemy path that would give an idea as to what the enemy will use to shoot down missiles with. Recon missiles are also useful for probing fleets that are orbiting a body.
If you want your survey fleet to be able to take out enemy survey ships and scouts, adding a beam fighter or two on the support carrier is reasonable. There is then a bit of a conflict between making a long endurance fighter for that or a high performance one. Long endurance means you can also use them as commerce raiders, going after slow and dispersed commercial ships.
The big thing you lose with a slower, long endurance fighter is the great reduction in their ability to contribute to point defense.