If you're going to run 4mm arrows, you don't have a lot of options. Here's my suggestion, run the Titanium half-outs from Easton. They basically take you from a "Deep Six" #6-40 thread to the "Standard" #8-32 thread which gives you a ton of options for broadheads AND a really strong/durable front end of your arrow. These half-outs weight 55 grains.
Easton’s 4MM Half-Out Titanium Insert enables the use of common 8-32 thread broadheads in 4MM Full Metal Jacket and 4MM Carbon Injexion shafts. Precision machined from TI-6 series titanium, this half-out delivers high strength-to-weight ratio. Included in your purchase is Easton’s HIT epoxy, which is recommended for the strongest bond and makes installation easy. The 4MM Half-Out provides a better tune than overly heavy steel half-outs and superior durability over aluminum half-outs. Easton’s HP extended design improves broadhead alignment for tighter groups.