According to details provided on Asus' official product page for the RX Vega Strix Gaming OC graphics card, it will be working at 1298MHz for the GPU base and 1590MHz for the GPU Boost clocks. This is around 50MHz higher than the standard/reference RX Vega running at 1247MHz GPU Base and 1546MHz GPU Boost clocks, and even lower than what we saw on the RX Vega 64 Liquid versions available earlier. The ROG RX Vega 64 Strix Gaming OC still packs 8GB of HBM2 memory running at 945MHz.
On the other hand, the custom Asus ROG RX Vega 64 Gaming OC comes with a custom triple-fan cooler with Asus' MaxContact GPU technology, FanConnect II and Asus Aura Sync RGB on top of it, which will probably do a whole lot better than the standard/reference blower-style cooler.
Unfortunately, the precise availability date or the price is still unknown but it will probably have a significant price premium compared to reference versions. Custom RX Vega 64 graphics cards are still nowhere to be seen as partners are still obviously fighting with supply issues.