Managed switch slower than unmanaged in same situation?

Hi there, 

Up until yesterday, I've been streaming high-speed video within my home successfully using a GS308 unmanaged switch - 1080p 120fps stream using Nvidia In-Home Streaming (via Moonlight). It was flawless.

This weekend I decided to swap in a managed switch (GS108Tv3, which isn't in the dropdown above so I've selected V2) in order to do some other, unrelated things involving VLANs. I've literally swapped the cables over - no other adjustments to the network or software stack. Network interfaces all still claim to be negotiating 1gig etc. But it kills the performance of the video stream dead - most of the frames dropped every time I move a window around. I know it's the switch config at fault somehow - I can swap back to the GS308 and it's instantly perfect again.

Can anyone help explain this? Is there some way that the GS108T, being a "business class" device, is worse at streaming video out of the box than the more basic switch?

Thoughts on what I could do? I've peeked in the QoS section and I basically get that one can apply policies to UDP and suchlike, but I'm lost in the complexity of queues, interfaces, Cos vs Qos and so on. Is there no way I can just turn it all off and get the same performance as the GS308?