You are correct - since the switch only does 1Gbit connectivity, the devices, including E-Series controller, will only do 1Gbit over any connection, meaning at most ~90MByte/sec speeds. If throughput is much below 70Mbyte/sec, you probably need to check and doublecheck all of your jumbo frame settings.
If you connect multiple connections on the vmware servers, you can use MPIO to balance IO somewhat over multiple connections, but it won't produce significant levels of improved throughput. For that, you would need a 10Gbit switch and cards for each of your vmware servers
On the E-Series of controllers, we do support Direct Connect for iSCSI for vmware, meaning you don't need a switch, but having one does allow for better resiliency and multipathing in your storage network. To get 10Gb connectivity, you will need appropriate cables (optical, twinax or 10GBaseT), supported by both controller and server, and ideally any future switch you get.
You can check the throughput you are geting with a tool like Atto disk benchmark in one of your VMs. This will generate lots of storage traffic which can be handy for finding issues and also check if changes you have made have had an impact.
That sounds more like a latency issue than a throughput issue as booting a server is unlikely to be maxing out a 1GB link.
Take a look at the delayed ack config.
Beyond that, I think you need to get familiar with the stats counters in vmware rather than relying solely on observing system performance.
Log in to vcenter, browse to your VM>monitor>perfromance then select disk from the drop down.
By default, this shows you the latency and throughput of your storage.
For flash storage, even over a 1GB link, you shouldn't be seeing much over 1ms in latency. For disk storage with no flash caching, expect to see not too much difference from your internal storage on the host (~20ms if busy, <10ms ideally)
I suspect that you will be seeing much higher values (ie. disable delayed ack)
Handy hint: vmware stats are accurate but the interface is slow and clunky. Get Veeam One (free), install on a windows box and point it at your virtual infrastructure. It will scoop up all your stats and give you a nice snappy interface to view up to 1 week of data. There are also a host of alarms you can confugure if you don't already have monitoring in place.