ArcExplorer much faster than desktop showing mosaic datasets and image services

Hello all

We have a large (300k tiles) mosaic dataset that is published as image service.
Consuming this service (or look directly on the mosaic dataset inside FGDB) is much quicker in ArcExplorer then in ArcMap.
This is true for new areas (where explorer does not have cache) or old places (that was viewed before).
ArcExplorer and ArcMap are running on the same machine with the same display size.
Is anybody else running into the same behavior?
Can somebody explain it or offer a way to make ArcMap as quick as ArcExplorer?

Thanks
Mody