Hey RL, its me again TorinoStyle!
I would surely stick with the 2V valve size so it does'nt hurt the torque. What happens is with the 2V head, you have a decent size port with a nice cross section thats not too big or not too small. With the bigger 4V size valves in it, the rapidly moving column of air/fuel mixture suddenly reaches this big wide open bowl with a big valve and the airflow is disrupted, causing the column of air to suddenly slow down before entering the cylinder. Since it enters at a slower speed, it starts to tumble and less of the air makes it into the cylinder.
The 2V size valve and bowl will hep keep the velocity up to speed where more of it will make it into the cylinder.
Hope Im not confusing you. This is what I have witnessed on a flowbench at a reputable race engine shop.