As a guideline, evolution wireless G3 systems can provide several hundred feet of reliable operation in a good RF environment. Your actual results in your location are a little hard to predict, as "it depends" on several factors.
The factors that will influence operating range include:
1. Output power.
Most Sennheiser transmitter's have 10 mW and 30 mW output modes. Greater output power allows you to transmit your signal further. You would need 100 mW to send your signal twice as far as a 10 mW signal.
2. The RF environment you are operating in.
Wireless microphone systems share the UHF spectrum with television stations, which will sound like static if your receiver tries to tune it. The background noise from television varies with transmitter distance and power, so we're always looking for the weakest signals (or vacant signals). Stronger signals will create more interference for your system.
3. People and humidity.
Transmitter antennas should never touch skin, skin contact will reduce RF range. Antennas should never be bent over, that will also detune the system and shorten range. Receiving antennas should be kept as high as possible,for best line of sight. You don't want to try sending the signal through a crowd, which absorbs RF, you'd prefer to sent it over their heads.
So as you can imagine, your performance in a remote area on a vacant television station frequency will be very different from your results in the center of London on a frequency shared with local television. Both will provide reliable results, but the operating range will be different.
The two key drivers of a wireless system are tuning bandwidth and output power, as both will help you avoid pockets of interference and gain reliable performance.